A color filter is produced by incorporating a polyfunctional monomer and a photopolymerization initiator, an alkali-soluble resin and other components to a pigment dispersion composition in which an organic pigment or inorganic pigment is dispersed to obtain a colored photosensitive composition, and carrying out a photolithographic method or the like using this composition.
In recent years, there has been a tendency for the usage of color filters in liquid crystal display (LCD) applications to expand to television (TV) sets in addition to monitors. With this tendency towards expanded use, there has been a demand for a high level of color characteristics in chromaticity, contrast and the like. Furthermore, there is also a similar demand for a high level of color characteristics in image sensor (solid state image pick-up element) applications.
In response to such demands as described above, it is required to disperse the pigment in a finer state (good dispersibility), and to disperse the pigment in a stable state (good dispersion stability). When the dispersibility is insufficient, there is a problem in that fringes (serration at the edge part) or surface unevenness occurs in the resulting colored resist film, thus causing a decrease in the chromaticity or dimensional accuracy of the color filters thus produced, or causing significant deterioration in the contrast. Furthermore, when dispersion stability is insufficient, it is likely that problems occur in the production process for color filters, particularly in that the uniformity of the film thickness is lowered in the process of applying a colored photosensitive composition, the sensitivity to light in the exposure process is decreased, or the alkali solubility in the development process is decreased. Furthermore, when the dispersion stability of the pigment is poor, there is a problem in that, along with the lapse of time, the constituent components of the colored photosensitive composition undergo aggregation and cause an increase in viscosity, so that the pot life becomes very short.
However, when the particle diameter of the pigment is made very small, the surface area of the pigment particles is increased. Accordingly, the cohesive force among the pigment particles is increased, so that it is often difficult to achieve a balance between dispersibility and dispersion stability at high level.
In order to solve such problems, various pigment dispersants have been developed.
For example, a polymeric pigment dispersant in which an organic dye is bound to a polymer has been disclosed (see, for example, Patent Document 1). In this regard, it is thought that since the interaction between the organic dye and the pigment particles introduced into the dispersant is enhanced, adsorption of the polymeric pigment dispersant onto the pigment particles is promoted, and thus the dispersibility is enhanced.
A polymeric pigment dispersant is also disclosed in which an organic dye or a heterocyclic ring is introduced only to one end or both ends of the polymer moiety (see, for example, Patent Documents 2 and 3). Patent Document 2 aims at securing an adsorption layer that is sufficient for dispersion stabilization, by efficiently achieving efficient adsorption of an organic dye or a heterocyclic ring onto the surface of a pigment, and also making the polymer moiety and the dispersion medium have sufficient affinity with each other, while Patent Document 3 achieves an improvement in synthesis technique over Patent Document 2 by using a chain transfer agent having an organic dye or a heterocyclic ring.
In addition, it is disclosed to improve the dispersibility by using an acrylic resin having a carboxylic acid group and adding a basic pigment derivative in which a dialkylamino group is introduced (see, for example, Patent Document 4). Moreover, a polymeric pigment dispersant is disclosed in which a sulfonic acid group or a monosulfuric acid ester group is introduced only to one end of the polymer moiety (see, for example, Patent Document 5). These aim at securing an adsorption layer that is sufficient for dispersion stabilization by allowing the surface of a pigment (particularly, a basic pigment) to efficiently adsorb sulfonic acid and also making the polymer moiety and the dispersion medium have sufficient affinity with each other.
Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 4-139262
Patent Document 2: JP-A No. 9-77987
Patent Document 3: JP-A No. 9-77994
Patent Document 4: JP-A No. 11-189732
Patent Document 5: JP-A No. 2002-273191